This crossover went from being fanboy wish to actual possibility when Pacific Rim: Uprising director Steven S. DeKnight was asked about its possibility by Collider, and gave this surprising response:

"...there’s been a lot of discussion about that possibility [of crossing over]. Look I think it would be fantastic to have the Pacific Rim universe join Legendary’s Monster Universe, it seems like a natural step. And part of the big overall plan after the third movie we’ve talked about is that could happen, it’s always a possibility. It’s by far not a certainty; it’s merely theoretical at this point, but as a fan myself I would love to see that happen.”

So say we all!

There's always been a certainly simplicity to both franchises that would make this crossover a worthy event. After all, fans just want to see big robots fighting big monsters; big monsters fighting other big monsters; and normal humans scrambling not to get crushed in the process. Given where both franchises are headed, it's not hard to imagine how this crossover could happen:

Slide 2/2 – How Pacific Rim Can Crossover With Godzilla/Kong

By the end of the Pacific Rim trilogy, it's not hard to imagine that the outcome will be that the Kaiju are destroyed or are no longer a threat, and Jaeger program can finally be ended for good, as humanity returns to more peaceful time and ways.

For Legendary Monster Universe, we know that Godzilla 2(which just wrapped production) will see the world invaded by even more Kaiju monsters from some realm near Earth's core (Rhodan, Mothra, King Ghidorah), and that the MONARCH organization will have to battle them - eventually with help from the big guy himself, Godzilla. Kong: Skull Island already established that both Godzilla and King Kong are from this subterranean world - and the two monster warriors will trade blows in Godzilla vs. Kong, which Death Note director Adam Winguard is directing for release in 2020.

With that big event film presumably ending with Godzilla and Kong forming a truce (instead of killing one another), we'd have the perfect setup for crossover with Pacific Rim!

Since both franchise hinge on monsters from other dimensions or unknown worlds appearing to torment humanity, it'd be easy to set up a story where a portal opens between the world of Pacific Rim and the world of monsters where Godzillaand Kong live. What would be especially interesting would be seeing Godzilla and Kong go from being the apex hunters in the world, to being the prey of some reactivated Jaegers. I'd watch that for a dollar - and millions of other fans probably would too.

Catch Pacific Rim: Uprising in theaters on March 23, 2018; Godzilla: King of Monsters in theaters on March 22, 2019, and Godzilla vs. Kong in theaters on May 22, 2020.